Thermal management systems generally include an enclosure such as a housing or cabinet for heat generating electronic component circuit cards or boards which must be cooled to prevent damage to the electronic components. A variable speed fan may be used to force air over the components and a temperature sensor and/or an air flow sensor monitors the temperature and/or air flow rate of the air or other cooling gas inside the cabinet.
A filter is used to reduce particulate matter in order to eliminate contaminants which could otherwise foul the circuit cards. A controller, connected to the fan and responsive to the temperature sensor and/or the air flow sensor, continuously monitors the temperature of the electronic circuit cards and may adjust the speed of the fan to keep the electronic components cool.
Such prior art systems, however, may detect temperature increases too late to gracefully shut down electronics being cooled. A graceful shut down would allow data to be saved prior to removing power to the electronics.
As circuitry has decreased in size, it is more sensitive to increases in temperature. Further, the resistance to airflow that such smaller circuitry presents is now comparable to that provided by filters. Thus, any blockage of a filter more quickly lowers airflow and adversely affects the circuitry. Common practice today is to schedule filter replacement on a set schedule, such as every six months. This practice does not take into account the environment where the filter may be located. In a dusty environment, the filter may need to be replaced more quickly. In a clean room environment, filter may last much longer than six months.
Further, prior art systems may utilize pressure sensor based airflow sensing in an effort to detect filter blockage. For airflow ranges seen in electronics enclosures, a pressure sensor with low measurement range is required. These sensors are large and susceptible to shock and vibration. They are also sensitive to mounting orientation. With smaller circuitry, the larger sensors become unwieldy and inaccurate. They may also fail to properly detect whether the filter is clogged to the point where cooling is no longer effective. Again, when the filter is clogged, the air flow rate through the cabinet may be less than optimal even at the highest fan speed resulting in component failure, thermal stress, or degradation which may not be detectable.